[PATCH] powerpc: Better pmd_bad() and pud_bad() checks

At present, the powerpc pmd_bad() and pud_bad() macros return false
unless the given pmd or pud is zero.  This patch makes these tests
more thorough, checking if the given pmd or pud looks like a plausible
pte page or pmd page pointer respectively.  This can result in helpful
error messages when messing with the pagetable code.
Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>

include/asm-powerpc/pgtable.h

@@ -188,9 +188,13 @@ static inline pte_t pfn_pte(unsigned long pfn, pgprot_t pgprot)
 #define pte_pfn(x)		((unsigned long)((pte_val(x)>>PTE_RPN_SHIFT)))
 #define pte_page(x)		pfn_to_page(pte_pfn(x))
 
+#define PMD_BAD_BITS		(PTE_TABLE_SIZE-1)
+#define PUD_BAD_BITS		(PMD_TABLE_SIZE-1)
+
 #define pmd_set(pmdp, pmdval) 	(pmd_val(*(pmdp)) = (pmdval))
 #define pmd_none(pmd)		(!pmd_val(pmd))
-#define	pmd_bad(pmd)		(pmd_val(pmd) == 0)
+#define	pmd_bad(pmd)		(!is_kernel_addr(pmd_val(pmd)) \
+				 || (pmd_val(pmd) & PMD_BAD_BITS))
 #define	pmd_present(pmd)	(pmd_val(pmd) != 0)
 #define	pmd_clear(pmdp)		(pmd_val(*(pmdp)) = 0)
 #define pmd_page_kernel(pmd)	(pmd_val(pmd) & ~PMD_MASKED_BITS)
@@ -198,7 +202,8 @@ static inline pte_t pfn_pte(unsigned long pfn, pgprot_t pgprot)
 
 #define pud_set(pudp, pudval)	(pud_val(*(pudp)) = (pudval))
 #define pud_none(pud)		(!pud_val(pud))
-#define pud_bad(pud)		((pud_val(pud)) == 0)
+#define	pud_bad(pud)		(!is_kernel_addr(pud_val(pud)) \
+				 || (pud_val(pud) & PUD_BAD_BITS))
 #define pud_present(pud)	(pud_val(pud) != 0)
 #define pud_clear(pudp)		(pud_val(*(pudp)) = 0)
 #define pud_page(pud)		(pud_val(pud) & ~PUD_MASKED_BITS)